Some communication systems use modulation schemes having rotated symbol constellations. In a rotated constellation, the real and imaginary components of the constellation symbols are typically not parallel with the axes of the signal space, but rather rotated at a certain angle relative to the axes.
Rotated constellations are used, for example, in DVB-T2 digital video broadcasting systems specified in “Digital Video Broadcasting (DVB); Frame Structure Channel Coding and Modulation for a Second Generation Digital Terrestrial Television Broadcasting System (DVB-T2),” DVB Document A122, July 2011, which is incorporated herein by reference. Constellation rotation is addressed, for example, in section 6.3.
Implementation guidelines for implementing constellation rotation in DVB-T2 systems are given in “Digital Video Broadcasting (DVB); Implementation Guidelines for a Second Generation Digital Terrestrial Television Broadcasting System (DVB-T2),” DVB Document A133, February 2012, which is incorporated herein by reference.
Li et al., describe example mapper and demapper designs for modulation and demodulation using rotated constellations, in “Design of Rotated QAM Mapper/Demapper for the DVB-T2 Standard,” IEEE Workshop on Signal Processing Systems (SiPS), Oct. 7-9, 2009, which is incorporated herein by reference.